C++ Casting

C++ Casting

C++에서 타입 변환, 캐스팅, 형 변환 이라고 다양하게 불리는 녀석을 정리!

cpp_casting_dt.vsdx

귀찮다고 사용한 C style 캐스팅으로인해 생긴 버그 때문에 밤새가며 어셈블리 코드와 씨름하기 싫다면...

*IMPORTANT* C style의 캐스팅은 절대 사용하지 말것!!

1. static_cast only succeeds if either the values are convertible or the pointers/references are compatible
2. dynamic_cast only casts between proper class hierarchic.
3. const_cast only works if source and target are cv-qualified versions of one another.
4. reinterpret_cast states explicitly that you wish to examine an underlying binary representation. Most "reinterpret_cast" can be eliminated with proper design. In other words "reinterpret_cast" is needed means, most-likely something is wrong in the design.

#include <iostream>

using namespace std;

class A { int x; };
class B { int y; };

class C : A, B { int z; };

int main()
{
  C c;

  // just type pun the pointer to c, pointer value will remain the same
  // only it's type is different.
  B *b1 = reinterpret_cast<B *>(&c);

  // perform the conversion with a semantic of static_cast<B*>(&c), disregarding
  // that B is an unaccessible base of C, resulting pointer will point
  // to the B sub-object in c.
  B *b2 = (B*)(&c);

  cout << "reinterpret_cast:\t" << b1 << "\n";
  cout << "C-style cast:\t\t" << b2 << "\n";
  cout << "no cast:\t\t" << &c << "\n";
}

and here is an output from ideone:

reinterpret_cast:  0xbfd84e78
C-style cast:      0xbfd84e7c 

no cast: 0xbfd84e78